Analysis of the pathway of L-trytophan biosynthesis has been valuable for the study of the relationship of genes and enzymes. Much is known about the pathway enzymes particularly in the Enterobacteriaceae, the bacterial family that includes Escherichia coli. However, the three-dimensional structure of none of the enzymes is available. Our first objective is to try and obtain a crystal suitable for X-ray diffraction of one of the pathway proteins irrespective of whether the amino acid sequence is known. We will start with the stable and easily purifiable proteins of Erwinia carotovora. The second objective is to study the evolution of anthranilate-5-phosphoribosylpyrophosphate phosphoribosyltransferase in the Enterobacteriaceae. In this family the enzyme exists in three strikingly different forms: a separate homodimer; a separate monomer; and covalently linked to glutamine amidotransferase. We have recently purified, and begun to analyze, one each of the separate forms. We propose to purify all the pathway enzymes from additional family genera, starting with Proteus, Aeromonas and two marine organisms Serratia marinorubra and Baneckea harveyi both for the evolution studies and to find suitable candidates for crystallization.